The present invention is generally directed to wireless communication systems and, more particularly, to a system and method for wireless communication using a symmetric communications protocol.
Wireless communication takes many forms ranging from two-way radios to cellular/PCS communication systems. The particular communication protocol depends on the specific wireless communication technology. For example, a cordless telephone, such as commonly used by consumers, comprises a base station and a single handset. The base station and handset communicate with each other on a preassigned frequency band. The base station is coupled to a public switched telephone network (PSTN) and functions as a master unit. The single handset function functions as a slave unit under the control of the master unit. With this communication protocol, the base station master unit generally transmits at full power and may send commands to the handset slave unit to control its transmission power.
Other communication systems, such as two-way radio systems, have no communication protocol. In these systems, one radio unit transmits and one or more radio units receive the transmitted message. The transmitting radio unit is activated by a pushed talk button, voice activated relay, or other conventional component. If transmitters in two radio units are activated simultaneously, a xe2x80x9ccollisionxe2x80x9d occurs with the resulting interference making reception difficult or impossible for the remaining receiving radio units.
In other communication systems, such as a specialized mobile radio (SMR), manufactured by companies such as Nextel, and Cellular/PCS systems, a base station communicates with one or more subscriber hand sets. The master-slave relationship in this type of communication system is fixed. That is, the base station always functions as the master unit and also serves as a gateway to the PSTN while the subscriber handsets function as slave units. With the master-slave communication arrangement described above, all communications must flow through the master unit. Thus, the master unit functions as a repeater when one slave unit communicates with another slave unit and functions as a gateway to the PSTN when one slave unit wishes to communicate via the PSTN.
The fixed master-slave relationship creates significant communication problems under certain conditions. For example, all slave units must be within range of the master unit to communicate with each other. Thus, communication between two slave units is impossible if one or both of the slave units are out of communication range of the master unit. This is true even when the slave units are within communication range of each other. Additional problems occur because the master unit typically transmits at maximum power levels. Such high signal levels can overload the low noise amplifier (LNA) and the radio frequency (RF) front end of nearby slave units. Such overloading renders the slave units incapable of communicating with other slave units that may be transmitting at low signal levels.
Therefore, it can be appreciated that there is a significant need for a communication system that eliminates the fixed master-slave relationship and its attending shortcomings. The present invention provides this and other advantages as will be apparent from the following description and accompanying figures.
The present invention is embodied in a system and method for symmetric communication protocol between two wireless communication units. The protocol does not require operation of a base station that is permanently designated as a master unit or the operation of remote units that are permanently designated as slave units. Instead, the calling unit is temporarily designated as a master unit and the called unit is designated as the slave. The calling unit and called unit both include signal monitors to monitor and determine the strength of received signals. If the received signal is above or below predetermined sets of limits, the wireless unit may transmit a power change request signal to the other unit.
The system may further include a base station coupled to a telephone network to permit wireless units to communicate with the telephone network via the base station. In an exemplary embodiment, the base station may be coupled to a public switched telephone network (PSTN) to allow units to communicate via the PSTN.
The units are programmed for operation at multiple frequencies. In an exemplary embodiment, a first unit transmits a request to communicate with a second unit using a selected subset of the operational frequencies. The second unit monitors at least one channel of the selected subset to detect the request to communicate. When a communication link is established between the units, the communication occurs over the entire set of operational frequencies. In one embodiment, the operational frequencies are selected in accordance with a pseudo-random sequence such that both units are programmed for operation in accordance with the pseudo-random sequence.
The initial communication may include a plurality of control data frames containing data to allow synchronization between the first and second units and to allow exchange of data relating to the pseudo-random sequence. The data frame also includes identification data indicating the second unit as a called party.
When a wireless communication link has been established, voice communications may occur bi-directionally using a plurality of message data frames. The message data frames include a provision for transmitting the power change request signal.